The Pavlovian conditioning of stimulus compounds has received extensive empirical and theoretical treatment in the past decade. Most investigators have been concerned only with the associations formed between the individual stimulus elements and the unconditioned stimulus. The proposed research examines other sources of responding in Pavlovian serial conditioning in rats. The first set of experiments investigates variables affecting the formation of associations among the elements of stimulus compounds. The use of an appetitive conditioning preparation involving direct behavioral observation of the subjects makes possible a separation of the roles of element-US and both mediated ("S-S") and unmediated ("S-R") within-compound associations in generating conditioned responding to serial compounds. A second set of experiments examines compound conditioning within simple conditional discriminations. Those experiments are especially concerned with the ability of stimuli in feature-positive and feature-negative discriminations to modulate the action of other associative units, independent of the participation of those stimuli in associations with the US or other stimulus elements.